Torque biasing systems can be implemented in vehicle components including, but not limited to, a transfer case, a power take-off unit (PTU) and an axle. Torque biasing systems regulate torque transfer between an input and an output. More specifically, a clutch pack is operably disposed between the input and the output. The degree of engagement of the clutch pack is varied to regulate the amount of torque transferred from the input to the output. For example, when the clutch pack is disengaged, there is no torque transfer from the input to the output. When the clutch pack is fully engaged or locked, all of the torque is transferred from the input to the output. When partially engaged, a corresponding portion of the torque is transferred from the input to the output.
The degree of clutch pack engagement is adjusted by a linear force that is imparted on the clutch pack via an actuator system. Traditional actuator systems include an electric motor and a clutch operator mechanism. The clutch operator mechanism converts the torque generated by the electric motor into the linear force, which can be amplified prior to being imparted on the clutch pack. The electric motor is controlled based on a control signal generated by a control system.
Conventional control systems use closed-loop control to regulate a specified system parameter. When the specified system parameter has an accurate means of feedback, such as is the case with direct sensing, the overall system accuracy is sufficient. In the case where the specified system parameter is not directly measurable, system accuracy is difficult to achieve.
Torque biasing systems are typically controlled based on a parameter other than torque, because torque is not easily measurable and torque sensors are not readily available. Torque sensors, however, would not be a total solution because the actual torque generated by a vehicle system is often much slower than is required by the biasing device. As a result, conventional torque biasing systems are not controlled as accurately as is desired.